Photoresist composition for deep ultraviolet lithography comprising a mixture of photoactive compounds

ABSTRACT

The present invention relates to a novel photoresist that can be developed with an aqueous alkaline solution, and is capable of being imaged at exposure wavelengths in the deep ultraviolet. The invention also relates to a process for imaging the novel photoresist. The novel photoresist comprises a) a polymer containing an acid labile group, and b) a novel mixture of photoactive compounds, where the mixture comprises a lower absorbing compound selected from structure 1 and 2, and a higher absorbing compound selected from structure 4 and 5,  
                 
 
     where, R 1  and R 2  are independently (C 1 -C 6 )alkyl, cycloalkyl, cyclohexanone, R 5 -R 9  are independently hydrogen, hydroxyl, (C 1 -C 6 )alkyl, C 1 -C 6 )aliphatic hydrocarbon containing one or more O atoms, m=1-5, X −  is an anion, and Ar is selected from naphthyl, anthracyl, and structure 3,  
                 
 
     where, R 3  is hydrogen or (C 1 -C 6 )alkyl, R 4  is independently hydrogen, (C 1 -C 6 )alkyl, (C 1 -C 6 )aliphatic hydrocarbon containing one or more O atoms, Y is a single bond or (C 1 -C 6 )alkyl, and n=1-4.

FIELD OF INVENTION

[0001] The present invention relates to a novel photoresist compositionthat is particularly useful in the field of microlithography, andespecially useful for imaging negative and positive patterns in theproduction of semiconductor devices. The photoresist compositioncomprises a copolymer and a photoactive component, where the photoactivecomponent comprises a mixture of an aromatic onium salt and an alkyarylonium salt. The novel photoresist composition provides both goodphotosensitivity and also significantly reduces edge roughness of theimaged photoresist profiles. Such a composition is especially useful forexposure at 193 nanometers (nm) and 157 nm. The invention furtherrelates to a process for imaging the novel photoresist.

BACKGROUND OF THE INVENTION

[0002] Photoresist compositions are used in microlithography processesfor making miniaturized electronic components such as in the fabricationof computer chips and integrated circuits. Generally, in theseprocesses, a thin coating of film of a photoresist composition is firstapplied to a substrate material, such as silicon wafers used for makingintegrated circuits. The coated substrate is then baked to evaporate anysolvent in the photoresist composition and to fix the coating onto thesubstrate. The photoresist coated on the substrate is next subjected toan image-wise exposure to radiation.

[0003] The radiation exposure causes a chemical transformation in theexposed areas of the coated surface. Visible light, ultraviolet (UV)light, electron beam and X-ray radiant energy are radiation typescommonly used today in microlithographic processes. After thisimage-wise exposure, the coated substrate is treated with a developersolution to dissolve and remove either the radiation exposed or theunexposed areas of the photoresist.

[0004] The trend toward the miniaturization of semiconductor devices hasled to the use of new photoresists that are sensitive at lower and lowerwavelengths of radiation and has also led to the use of sophisticatedmultilevel systems to overcome difficulties associated with suchminiaturization.

[0005] There are two types of photoresist compositions: negative-workingand positive-working. The type of photoresist used at a particular pointin lithographic processing is determined by the design of thesemiconductor device. When negative-working photoresist compositions areexposed image-wise to radiation, the areas of the photoresistcomposition exposed to the radiation become less soluble to a developersolution (e.g. a cross-linking reaction occurs) while the unexposedareas of the photoresist coating remain relatively soluble to such asolution. Thus, treatment of an exposed negative-working resist with adeveloper causes removal of the non-exposed areas of the photoresistcoating and the creation of a negative image in the coating, therebyuncovering a desired portion of the underlying substrate surface onwhich the photoresist composition was deposited.

[0006] On the other hand, when positive-working photoresist compositionsare exposed image-wise to radiation, those areas of the photoresistcomposition exposed to the radiation become more soluble to thedeveloper solution (e.g. a rearrangement reaction occurs) while thoseareas not exposed remain relatively insoluble to the developer solution.Thus, treatment of an exposed positive-working photoresist with thedeveloper causes removal of the exposed areas of the coating and thecreation of a positive image in the photoresist coating. Again, adesired portion of the underlying surface is uncovered.

[0007] Photoresist resolution is defined as the smallest feature, whichthe resist composition can transfer from the photomask to the substratewith a high degree of image edge acuity after exposure and development.In many leading edge manufacturing applications today, photoresistresolution on the order of less than one-half micron are necessary. Inaddition, it is almost always desirable that the developed photoresistwall profiles be near vertical relative to the substrate. Suchdemarcations between developed and undeveloped areas of the resistcoating translate into accurate pattern transfer of the mask image ontothe substrate. This becomes even more critical as the push towardminiaturization reduces the critical dimensions on the devices. In caseswhere the photoresist dimensions have been reduced to below 150nanometer(nm), the roughness of the photoresist patterns has become acritical issue. Edge roughness, commonly known as line edge roughness,is typically observed for line and space patterns as roughness along thephotoresist line, and for contact holes as side wall roughness. Edgeroughness can have adverse effects on the lithographic performance ofthe photoresist, especially in reducing the critical dimension latitudeand also in transferring the line edge roughness of the photoresist tothe substrate. Hence, photoresists that minimize edge roughness arehighly desirable.

[0008] Photoresists sensitive to short wavelengths, between about 100 nmand about 300 nm are often used where subhalfmicron geometries arerequired. Particularly preferred are photoresists comprisingnon-aromatic polymers, a photoacid generator, optionally a dissolutioninhibitor, and solvent.

[0009] High resolution, chemically amplified, deep ultraviolet (100-300nm) positive and negative tone photoresists are available for patterningimages with less than quarter micron geometries. To date, there arethree major deep ultraviolet (uv) exposure technologies that haveprovided significant advancement in miniaturization, and these uselasers that emit radiation at 248 nm, 193 nm and 157 nm. Photoresistsused in the deep uv typically comprise a polymer which has an acidlabile group and which can deprotect in the presence of an acid, aphotoactive component which generates an acid upon absorption of light,and a solvent.

[0010] Photoresists for 248 nm have typically been based on substitutedpolyhydroxystyrene and its copolymers, such as those described in U.S.Pat. No. 4,491,628 and U.S. Pat. No. 5,350,660. On the other hand,photoresists for 193 nm exposure require non-aromatic polymers, sincearomatics are opaque at this wavelength. U.S. Pat. No. 5,843,624 and GB2,320,718 disclose photoresists useful for 193 nm exposure. Generally,polymers containing alicyclic hydrocarbons are used for photoresists forexposure below 200 nm. Alicyclic hydrocarbons are incorporated into thepolymer for many reasons, primarily since they have relatively highcarbon:hydrogen ratios which improve etch resistance, they also providetransparency at low wavelengths and they have relatively high glasstransition temperatures. Photoresists sensitive at 157 nm have beenbased on fluorinated polymers, which are known to be substantiallytransparent at that wavelength. Photoresists derived from polymerscontaining fluorinated groups are described in WO 00/67072 and WO00/17712.

[0011] The polymers used in a photoresist are designed to be transparentto the imaging wavelength, but on the other hand, the photoactivecomponent has been typically designed to be absorbing at the imagingwavelength to maximize photosensitivity. The photosensitivity of thephotoresist is dependent on the absorption characteristics of thephotoactive component, the higher the absorption the less the energyrequired to generate the acid and the more photosensitive thephotoresist is. Aromatic photoactive compounds, such as triphenylsulfonium salts, diphenyl iodonium salts are known to give goodphotosensitivity at 248 nm, but have found to be too absorbing atwavelengths below 200 nm and lead to tapered photoresist profiles.Transparent sulfonium salts based on alkyl sulfonium salts have found tobe too transparent at the imaging wavelength and result in poorphotosensitivity. JP 10319581, EP 1,085,377, EP 1,041,442, and U.S. Pat.No. 6,187,504 disclose alkylaryl sulfonium salts of different structuresthat can be used in the photoresist composition.

[0012] The inventors of this application have found that the photoactivecompounds known in the prior art cause unacceptable levels of line edgeroughness, or if the line edge roughness is acceptable then thephotosensitivity is poor. However, the inventors of this applicationhave also found that if a mixture of a specific alkylarylsulfonium oralkylaryliodonium salt and an arylsulfonium or aryliodonium salt isused, the line edge roughness is significantly reduced while maintainingan acceptable level of photosensitivity. EP 1,085,377 discloses thatmixtures of alkylarylsulfonium salts may be used with other onium salts,diazomethane derivatives, glyoxime derivatives and many otherphotoactive compounds. A specific mixture of photoactive compounds isnot disclosed which when formulated into a photoresist wouldsignificantly reduce line edge roughness.

[0013] The object of this invention is to provide a novel photoresistcomposition, which can provide good lithographic performance especiallyin reducing line edge roughness while maintaining good photosensitivity.

[0014] The present invention pertains to a novel photoresist compositioncomprising a polymer and a novel mixture of photosensitive compounds.The composition is particularly useful for imaging in the range of100-300 nm, and more particularly for 157 nm and 193 nm.

SUMMARY OF THE INVENTION

[0015] The present invention relates to a novel photoresist compositionuseful for imaging in deep uv comprising a) a polymer containing an acidlabile group, and, b) a novel mixture of photoactive compounds, wherethe mixture comprises a lower absorbing compound selected from structure1 and 2, and a higher absorbing compound selected from structure 4 and5,

[0016] where, R₁ and R₂ are independently (C₁-C₆)alkyl, cycloalkyl,cyclohexanone, R₅-R₉ are independently hydrogen, hydroxyl, (C₁-C₆)alkyl,and (C₁-C₆)aliphatic hydrocarbon containing one or more O atoms, m=1-5,X⁻ is an anion, and Ar is selected from naphthyl, anthracyl, andstructure 3,

[0017] where, R₃ is hydrogen or (C₁-C₆)alkyl, R₄ is independentlyhydrogen, (C₁-C₆)alkyl, (C₁-C₆)aliphatic hydrocarbon containing one ormore 0 atoms, Y is a single bond or (C₁-C₆)alkyl, and n=1-4.

[0018] The invention also relates to a process for imaging a photoresistcomprising the steps of a) forming on a substrate a photoresist coatingfrom the novel photoresist composition, b) image-wise exposing thephotoresist coating, c) optionally, postexposure baking the photoresistcoating, and d) developing the photoresist coating with an aqueousalkaline solution.

DESCRIPTION OF THE INVENTION

[0019] The present invention relates to a novel photoresist that can bedeveloped with an aqueous alkaline solution, and is capable of beingimaged at exposure wavelengths below 200 nm. The invention also relatesto a process for imaging the novel photoresist. The novel photoresistcomprises a) a polymer containing an acid labile group, and b) a novelmixture of photoactive compounds, where the mixture comprises a higherabsorbing compound selected from an aromatic sulfonium salt (structure4) and an aromatic iodonium salt (structure 5) and a lower absorbingcompound selected from structure 1 and 2.

[0020] where, R₁ and R₂ are independently (C₁-C₆)alkyl, cycloalkyl,cyclohexanone, R₅-R₉ are independently hydrogen, hydroxyl, (C₁-C₆)alkyl,and (C₁-C₆)aliphatic hydrocarbon containing one or more O atoms, m=1-5,X⁻ is an anion, and Ar is selected from naphthyl, anthracyl andstructure 3,

[0021] where, R₃ is hydrogen or (C₁-C₆)alkyl, R₄ is independentlyhydrogen, (C₁-C₆)alkyl, (C₁-C₆)aliphatic hydrocarbon containing one ormore O atoms, Y is a single bond or (C₁-C₆)alkyl, and n=1-4.

[0022] The aromatic sulfonium salts, such as triphenyl sulfonium salt,derivatives of triphenyl sulfonium salt, diphenyl iodonium salt andderivatives of diphenyl iodonium salt, provide the higher absorbingcomponent, while the compounds of structure 1 or 2 provide the lowerabsorbing component. It has unexpectedly been found that by combining ahigher absorbing photoactive component with a lower absorbingphotoactive component that the edge roughness of the photoresist patterncan be greatly reduced while maintaining acceptable photosensitivity. Ithas further been found that the optimum lithographic performance isobtained when the ratio of the higher absorbing component and the lowerabsorbing component is in the molar ratio 1:2 to 2:1, and preferablyabout 1:1. Line edge roughness improvement of greater than 20% isacceptable, greater than 35% is preferable, greater than 50% is morepreferable and greater than 75% is most preferable. Acceptable levels ofline edge roughness are obtained while maintaining good photosensitivityby using the components of this invention.

[0023] The higher absorbing photoactive components are aromatic iodoniumand sulfonium salts of structure 4 and 5.

[0024] where, R₅-R₉ are independently hydrogen, hydroxyl, (C₁-C₆)alkyl,and (C₁-C₆)aliphatic hydrocarbon containing one or more O atoms, m=1-5,and X⁻ is an anion. Examples are diphenyliodonium salts,triphenylsulfonium salts and the like. Examples of X⁻ aretrifluoromethane sulfonate (triflate),1,1,1,2,3,3-hexafluoropropanesulfonate, perfluorobutanebutanesulfonate(nonaflate), camphor sulfonate, perfluorooctane sulfonate, benzenesulfonate and toluenesulfonate. Some examples, without limitation are,of sulfonium salts are triphenylsulfonium salts, trialkylphenylsulfoniumsalts, (p-tert-butoxyphenyl)triphenylsulfonium salts,bis(p-tert-butoxyphenyl)phenylsulfonium salts, andtris(p-tert-butoxyphenyl)sulfonium salts. Some examples, withoutlimitation, of iodonium salts are diphenyliodonium salts,di(alkylphenyl)iodonium salts etc. The counter ion, X⁻, may be any ionthat gives good lithographic properties, and examples of which arefluoroalkylsulfonates such as 1,1,1-trifluoromethanesulfonate andnonafluorobutanesulfonate, arylsulfonates such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate, and alkylsulfonates such asmesylate and butanesulfonate. Preferred salts are diphenyliodoniumtrifluoromethane sulfonate, diphenyliodonium nonafluorobutanesufonate,triphenylsulfonium trifluromethanesuflonate, and triphenylsulfoniumnonafluorobutanesufonate.

[0025] The lower absorbing photoactive component is a compound ofstructure 1 or 2.

[0026] where, R₁ and R₂ are independently (C₁-C₆)alkyl, cycloalkyl,cyclohexanone, X⁻ is an anion, and Ar is selected from naphthyl,anthracyl, and structure 3,

[0027] where, R₃ is hydrogen or (C₁-C₆)alkyl, R₄ is independentlyhydrogen, (C₁-C₆)alkyl, (C₁-C₆)aliphatic hydrocarbon containing one ormore O atoms, Y is a single bond or (C₁-C₆)alkyl, and n=1-4.

[0028] The alkyl group generally has up to 6 linear or branched carbonatoms and can be groups such as methyl, ethyl, propyl, butyl, pentyl,hexyl, isopropyl, and t-butyl. The (C₁-C₆)aliphatic hydrocarboncontaining one or more O atoms can be any alkyl group with linkages suchas ether, keto, carboxyl, or other O based linkages. The cycloalkylgroup has up to 16 carbon atoms, examples of which are cyclopentyl,cyclohexyl, cyclooctyl, norbornyl, isonorbornyl and adamantyl. Thearomatic group, Ar, may be connected directly to the sulfonium ion orhave a linking alkylene group with up to 6 alkyl carbon atoms. Thearomatic group may be phenyl, naphthyl or anthracyl and theirderivatives. The phenyl group has the structure 3, examples of which are4-methoxyphenyl, 4-hydroxyphenyl, 3,5-dimethyl, 4-hydroxyphenyl and3,5-dimethyl,4-methoxyphenyl. Other groups that illustrate thederivatives of the naphthyl and anthracyl functionality, but are notlimited to, are alkylnaphthyl, dialkylnaphthyl, alkylanthracyl,dialkylanthracyl, alkoxynaphthyl, alkoxyanthracyl, dialkoxynaphthyl,dialkoxyanthracyl examples of which are methylnaphthyl, ethylnaphthyl,methylanthracyl, ethylanthracyl, methoxy naphthyl, ethoxynaphthyl,methoxynaphthyl, ethoxyanthracyl and others.

[0029] In one of the preferred embodiments Y is a single bond, in which,the aromatic group is connected directly to the sulfonium ion, and thearomatic group is phenyl or substituted phenyl, preferablymethoxydimethylphenyl dimethyl sulfonium salts, methoxyphenyldimethylsulfonium salts, hydroxydimethylphenyl dimethyl sulfonium salts,and hydroxyphenyl dimethylsulfonium salts.

[0030] Examples of the lower absorbing photoactive compound, withoutlimitations, are 4-methoxyphenyl-dimethylsulfonium triflate,3,5-dimethyl-4-hydroxyphenyl-dimethyl sulfonium triflate,3,5-dimethyl-4-methoxyphenyl-dimethyl sulfonium triflate,3,5-dimethyl-4-hydroxyphenyl-dimethyl sulfonium nonaflate,3,5-dimethyl-4-methoxyphenyl-dimethyl sulfonium nonaflate,4-methoxyphenyl-methyliodonium triflate or nonaflate,3,5-dimethyl-4-hydroxyphenyl-methyliodonium triflate or nonaflate, and3,5-dimethyl-4-methoxyphenyl-methyl iodonium triflate or nonaflate.

[0031] One of the preferred mixtures of photoactive compounds is amixture of triphenylsulfonium triflate or nonaflate with3,5-dimethyl,4-methoxyphenylsulfonium triflate or nonaflate.

[0032] The polymer of the invention is one that has acid labile groupsthat make the polymer insoluble in aqueous alkaline solution, but such apolymer in the presence of an acid catalytically deprotects the polymer,wherein the polymer then becomes soluble in an aqueous alkalinesolution. The polymers preferably are transparent below 200 nm, and areessentially non-aromatic, and preferably are acrylates and/orcycloolefin polymers. Such polymers are, for example, but not limitedto, those described in U.S. Pat. No. 5,843,624, U.S. Pat. No. 5,879,857,WO 97/33,198, EP 789,278 and GB 2,332,679. Nonaromatic polymers that arepreferred for irradiation below 200 nm are substituted acrylates,cycloolefins, substituted polyethylenes, etc. Aromatic polymers based onpolyhydroxystyrene and its copolymers may also be used, especially for248 nm exposure. Preferred comonomers are methacrylates.

[0033] Polymers based on acrylates are generally based onpoly(meth)acrylates with at least one unit containing pendant alicyclicgroups, and with the acid labile group being pendant from the polymerbackbone and/or from the alicyclic group. Examples of pendant alicyclicgroups, may be adamantyl, tricyclodecyl, isobornyl, menthyl and theirderivatives. Other pendant groups may also be incorporated into thepolymer, such as mevalonic lactone, gamma butyrolactone, alkyloxyalkyl,etc. More preferred structures for the alicyclic group are:

[0034] The type of monomers and their ratios incorporated into thepolymer are optimized to give the best lithographic performance. Suchpolymers are described in R. R. Dammel et al., Advances in ResistTechnology and Processing, SPIE, Vol. 3333, p144, (1998). Examples ofthese polymers include poly(2-methyl-2-adamantanemethacrylate-co-mevalonic lactone methacrylate),poly(carboxy-tetracyclododecylmethacrylate-co-tetrahydropyranylcarboxytetracyclododecyl methacrylate),poly(tricyclodecylacrylate-co-tetrahydropyranylmethacrylate-co-methacrylicacid),poly(3-oxocyclohexyl methacrylate-co-adamantylmethacrylate).

[0035] Polymers synthesized from cycloolefins, with norbornene andtetracyclododecene derivatives, may be polymerized by ring-openingmetathesis, free-radical polymerization or using metal organiccatalysts. Cycloolefin derivatives may also be copolymerized with cyclicanhydrides or with maleimide or its derivatives. Examples of cyclicanhydrides are maleic anhydride and itaconic anhydride. The cycloolefinis incorporated into the backbone of the polymer and may be anysubstituted or unsubstituted multicyclic hydrocarbon containing anunsaturated bond. The monomer can have acid labile groups attached. Thepolymer may be synthesized from one or more cyclo olefin monomers havingan unsaturated bond. The cyclo olefin monomers may be substituted orunsubstituted norbornene, or tetracyclododecane. The substituents on thecyclo olefin may be aliphatic or cycloaliphatic alkyls, esters, acids,hydroxyl, nitrile or alkyl derivatives. Examples of cyclo olefinmonomers, without limitation, are:

[0036] Other cyclo olefin monomers which may also be used insynthesizing the polymer are:

[0037] Such polymers are described in the following reference andincorporated herein, M-D. Rahman et al, Advances in Resist Technologyand Processing, SPIE, Vol. 3678, p1193, (1999). Examples of thesepolymers include poly((t-butyl5-norbornene-2-carboxylate-co-2-hydroxyethyl5-norbornene-2-carboxylate-co-5-norbornene-2-carboxylic acid-co-maleican hydride), poly(t-butyl5-norbornene-2-carboxylate-co-isobornyl-5-norbornene-2-carboxylate-co-2-hydroxyethyl5-norbornene-2-carboxylate-co-5-norbornene-2-carboxylic acid-co-maleicanhydride), poly(tetracyclododecene-5-carboxylate-co-maleic anhydride),poly(t-butyl 5-norbornene-2-carboxylate-co-maleicanhydride-co-2-methyladamantyl methacrylate-co-2-mevalonic lactonemethacrylate), poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacylate) and the like.

[0038] Polymers containing mixtures of acrylate monomers, cycloolefinicmonomers and cyclic anhydrides, where such monomers are described above,may also be combined into a hybrid polymer. Preferably the cyclo olefinmonomer is selected from t-butyl norbornene carboxylate (BNC),hydroxyethyl norbornene carboxylate (HNC), norbornene carboxylicacid(NC), t-butyl tetracyclo[4.4.0.1.^(2,6)1.^(7,10)]dodec-8-ene-3-carboxylate, and t-butoxycarbonylmethyltetracyclo[4.4.0.1.^(2,6)1.^(7,10)] dodec-8-ene-3-carboxylate; morepreferably the cyclo olefins are selected from t-butyl norbornenecarboxylate (BNC), hydroxyethyl norbornene carboxylate (HNC), andnorbornene carboxylic acid(NC). The preferred acrylate monomers areselected from mevaloniclactone methacrylate (MLMA), 2-methyladamantylmethacrylate (MAdMA), isoadamantyl methacrylate,3-hydroxy-1-methacryloxyadamatane,3,5-dihydroxy-1-methacryloxyadamantane, β-methacryloxy-γ-butyrolactone,and α-methacryloxy-γ-butyrolactone. More preferably the acrylatemonomers are selected from mevaloniclactone methacrylate (MLMA) and2-methyladamantyl methacrylate (MAdMA). The cyclic anhydride ispreferably maleic anhydride.

[0039] The cyclo olefin and the cyclic anhydride monomer are believed toform an alternating polymeric structure, and the amount of the acrylatemonomer incorporated into the polymer can be varied to give the optimallithographic properties. The percentage of the acrylate monomer relativeto the cyclo olefin/anhydride monomers within the polymer ranges fromabout 95 mole % to about 5 mole %, preferably from about 75 mole % toabout 25 mole %, and most preferably from about 55 mole % to about 45mole %.

[0040] Fluorinated non-phenolic polymers, useful for 157 nm exposure,also exhibit line edge roughness and can benefit from the use of thenovel mixture of photoactive compounds described in the presentinvention. Such polymers are described in WO 00/17712 and WO 00/67072and incorporated herein by reference. Example of one such polymer ispoly(tetrafluoroethylene-co-norbornene-co-5-hexafluoroisopropanol-substituted2-norbornene.

[0041] Polymers synthesized from cycloolefins and cyano containingethylenic monomers are described in the U.S. patent application Ser. No.09/854,312 and incorporated herein by reference, may also be used.

[0042] The molecular weight of the polymers is optimized based on thetype of chemistry used and on the lithographic performance desired.Typically, the weight average molecular weight is in the range of 3,000to 30,000 and the polydispersity is in the range 1.1 to 5, preferably1.5 to 2.5.

[0043] The solid components of the present invention are dissolved in anorganic solvent. The amount of solids in the solvent or mixture ofsolvents ranges from about 5 weight% to about 50 weight%. The polymermay be in the range of 5 weight% to 90 weight% of the solids and thephotoacid generator may be in the range of 2 weight% to about 50 weight%of the solids. Suitable solvents for such photoresists may includepropylene glycol mono-alkyl ether, propylene glycol alkyl (e.g. methyl)ether acetate, ethyl-3-ethoxypropionate, xylene, diglyme, amyl acetate,ethyl lactate, butyl acetate, 2-heptanone, ethylene glycol monoethylether acetate, and mixtures thereof.

[0044] Various other additives such as colorants, non-actinic dyes,anti-striation agents, plasticizers, adhesion promoters, dissolutioninhibitors, coating aids, photospeed enhancers and surfactants may beadded to the photoresist composition before the solution is coated ontoa substrate. Surfactants that improve film thickness uniformity, such asfluorinated surfactants, can be added to the photoresist solution. Asensitizer that transfers energy from a particular range of wavelengthsto a different exposure wavelength may also be added to the photoresistcomposition. Often bases are also added to the photoresist to preventt-tops or bridging at the surface of the photoresist image. Examples ofbases are amines, ammonium hydroxide, and photosensitive bases.Particularly preferred bases are trioctylamine, diethanolamine andtetrabutylammonium hydroxide.

[0045] The prepared photoresist composition solution can be applied to asubstrate by any conventional method used in the photoresist art,including dipping, spraying, and spin coating. When spin coating, forexample, the photoresist solution can be adjusted with respect to thepercentage of solids content, in order to provide coating of the desiredthickness, given the type of spinning equipment utilized and the amountof time allowed for the spinning process. Suitable substrates includesilicon, aluminum, polymeric resins, silicon dioxide, doped silicondioxide, silicon nitride, tantalum, copper, polysilicon, ceramics,aluminum/copper mixtures; gallium arsenide and other such Group III/Vcompounds. The photoresist may also be coated over antireflectivecoatings.

[0046] The photoresist coatings produced by the described procedure areparticularly suitable for application to silicon/silicon dioxide wafers,such as are utilized in the production of microprocessors and otherminiaturized integrated circuit components. An aluminum/aluminum oxidewafer can also be used. The substrate may also comprise variouspolymeric resins, especially transparent polymers such as polyesters.

[0047] The photoresist composition solution is then coated onto thesubstrate, and the substrate is treated at a temperature from about 70°C. to about 150° C. for from about 30 seconds to about 180 seconds on ahot plate or for from about 15 to about 90 minutes in a convection oven.This temperature treatment is selected in order to reduce theconcentration of residual solvents in the photoresist, while not causingsubstantial thermal degradation of the solid components. In general, onedesires to minimize the concentration of solvents and this firsttemperature. Treatment is conducted until substantially all of thesolvents have evaporated and a thin coating of photoresist composition,on the order of half a micron (micrometer) in thickness, remains on thesubstrate. In a preferred embodiment the temperature is from about 95°C. to about 120° C. The treatment is conducted until the rate of changeof solvent removal becomes relatively insignificant. The film thickness,temperature and time selection depends on the photoresist propertiesdesired by the user, as well as the equipment used and commerciallydesired coating times. The coated substrate can then be imagewiseexposed to actinic radiation, e.g., ultraviolet radiation, at awavelength of from about 100 nm (nanometers) to about 300 nm, x-ray,electron beam, ion beam or laser radiation, in any desired pattern,produced by use of suitable masks, negatives, stencils, templates, etc.

[0048] The photoresist is then subjected to a post exposure secondbaking or heat treatment before development. The heating temperaturesmay range from about 90° C. to about 150° C., more preferably from about100° C. to about 130° C. The heating may be conducted for from about 30seconds to about 2 minutes, more preferably from about 60 seconds toabout 90 seconds on a hot plate or about 30 to about 45 minutes byconvection oven.

[0049] The exposed photoresist-coated substrates are developed to removethe image-wise exposed areas by immersion in a developing solution ordeveloped by spray development process. The solution is preferablyagitated, for example, by nitrogen burst agitation. The substrates areallowed to remain in the developer until all, or substantially all, ofthe photoresist coating has dissolved from the exposed areas. Developersinclude aqueous solutions of ammonium or alkali metal hydroxides. Onepreferred developer is an aqueous solution of tetramethyl ammoniumhydroxide. After removal of the coated wafers from the developingsolution, one may conduct an optional post-development heat treatment orbake to increase the coating's adhesion and chemical resistance toetching conditions and other substances. The post-development heattreatment can comprise the oven baking of the coating and substratebelow the coating's softening point or UV hardening process. Inindustrial applications, particularly in the manufacture ofmicrocircuitry units on silicon/silicon dioxide-type substrates, thedeveloped substrates may be treated with a buffered, hydrofluoric acidbase etching solution or dry etching. Prior to dry etching thephotoresist may be treated to electron beam curing in order to increasethe dry-etch resistance of the photoresist.

[0050] Each of the documents referred to above are incorporated hereinby reference in its entirety, for all purposes. The following specificexamples will provide detailed illustrations of the methods of producingand utilizing compositions of the present invention. These examples arenot intended, however, to limit or restrict the scope of the inventionin any way and should not be construed as providing conditions,parameters or values which must be utilized exclusively in order topractice the present invention. Unless otherwise specified, all partsand percents are by weight.

EXAMPLES

[0051] The refractive index (n) and the absorption (k) values of thephotoresist in the Examples below were measured on a J. A. WoollamVASE32 ellipsometer.

[0052] The triphenyl sulfonium nonafluorobutane sulfonate used in thephotoresist formulation is available from Toyo Gosei Company Ltd. Japan.

[0053] The line edge roughness (LER) was measured on a KLA8100 CD SEMtool using 600V acceleration voltage, 100K magnification and with athreshold of 50%. The length of the photoresist line measured was 1.5μm. LER was the (3σ) value calculated using 24 data points on each sideof the photoresist line.

Synthetic Example 1 Synthesis of 4-methoxyphenyl Dimethyl SulfoniumTriflate

[0054] To a 500 ml round bottomed flask equipped with a thermometer, amechanical stirrer, and a condenser, 1-methoxy-4-(methylthio) benzene(25 g, 0.162 mole), silver triflate (42.2 g, 0.164 mole) and 300 gtetrahydrohydrofuran (THF) were added. The mixture was heated at 40° C.to dissolve all the solids. A clear solution was cooled to roomtemperature and iodomethane (23.5 g, 0.166 mole) was added dropwise froma dropping funnel. The precipitate formed immediately during theaddition of iodomethane. An exotherm was observed and the temperaturerose to 55° C. The reaction mixture was stirred for 4 hours and theprecipitate was filtered out. The solution was dark and the THF wasreduced under vacuum. The solution was added drop wise to one liter ofether. The precipitate was dissolved in dichloromethane (200 ml) andfiltered to remove silver oxide. The filtrate was drowned in ether (1liter) and the white precipitate was filtered and dried under vacuum at35° C. (white crystals). The yield was 16.0 g (33%). The solid productgave the following analytical ¹H NMR(Acetone-d6) results: 3.43 (s, 6H,2CH₃); 3.93 (s, 3H, OCH₃); 7.29 (d, 2H, aromatic); 8.13 (d, 2H,aromatic). The absorptivity was 71.21 L/g.cm.

Synthetic Example 2 4-Hydroxy-3,5-dimethyl Phenyl Dimethyl SulphoniumChloride

[0055] 61 g of dimethylphenol (0.5 mole), 39 g (0.5 mole) ofdimethylsulfoxide (DMSO), and 400 ml of methanol were placed in a 1liter round bottom flask equipped with a thermometer and a condenser.The mixture was cooled in a liquid nitrogen-isopropyl alcohol bath whilehydrogen chloride gas was bubbled in at 10° C. for 6 hours. Aprecipitate was formed and a part of the methanol was removed byrotavap. The crystals were filtered and washed with ether several times.The solid product gave the following analytical results ¹HNMR(Acetone-d6), 2.34 (s, 6H, 2CH₃); 3.23 (s, 6H, 2CH₃); 7.80 (s, 2H,aromatic).

Synthetic Example 3 4-Hydroxy-3,5-dimethyl Phenyl Dimethyl SulphoniumTriflate

[0056] 2.185 g of 4-Hydroxy-3,5-dimethyl phenyl dimethyl sulphoniumchloride were placed in a flask and 10 g of water were added, followedby 2.56 g of silver trifluoro methane sulfonate in acetone. Aprecipitate of AgCl formed immediately. The mixture was stirred for 30minutes and the precipitate was filtered off. The solution was extractedwith dichloromethane, dried over sodium sulphate and filtered. Thesolution was drowned into ether and a precipitate formed which wasfiltered and dried in the vacuum dryer at less than 40° C. The solidproduct gave the following analytical results: ¹H NMR(Acetone-d6), 2.40(s, 6H, 2CH₃); 3.10 (s, 6H, 2CH₃); 7.65 (s, 2H, aromatic).

Synthetic Example 4 4-Methoxy-3,5-dimethyl Phenyl Dimethyl SulphoniumTriflate

[0057] 4-Hydroxy-3,5-dimethyl phenyl dimethyl sulphonium chloride (10.0g, 0.054 mole) was placed in a 250 ml round bottom flask with a stirrer,a condenser and a thermowatch. Deionized water (100 ml) and 3.4 g ofNaOH (50%) were added. Dimethyl sulphate (6.8 g 0.054 mole) was addedwith a syringe. The mixture was stirred at room temperature for 20minutes and then heated at 55° C. for 4 hours. After neutralization thereaction mix was added to acetone, and the salt precipitated out, whichwas filtered. The crude product in water was treated with silvertrifluoromethane sulfonate and silver chloride was precipitated out.After filtering the salt, the solution was extracted withdichloromethane. The dichloromethane layer was washed with water, driedover sodium sulphate and drowned in ether. The precipitate was filteredand washed with ether. It was dried under vacuum. The solid product gavethe following analytical results: ¹H NMR(Acetone-d6), 2.40 (s, 6H,2CH₃);3.47 (s, 6H, 2CH₃); 3.85 (s, 3H, OCH₃); 7.89 (d, 2H, aromatic).

Synthetic Example 5 4-Hydroxy-3,5-dimethyl Phenyl Dimethyl SulphoniumNonaflate

[0058] 2.185 g of 4-Hydroxy-3,5-dimethyl phenyl dimethyl sulphonium, 100g water, and 3.38 g of potassium perflouro butane sulfonate in acetonewere added in a flask. A precipitate formed immediately. The mixture wasstirred for 30 minutes, the solution was extracted with dichloromethane,dried over sodium sulphate and filtered. The solution was drowned intoether, a precipitate was formed, filtered and dried in the vacuum dryerat less than 40° C. The solid product gave the following analyticalresults: ¹H NMR(Acetone-d6), 2.32 (s, 6H, 2CH₃); 3.4 (s, 6H, 2CH₃); 7.78(s, 2H, aromatic). The absorptivity was 56.15 L/g.cm.

Synthetic Example 6 4-Methoxy-3,5-dimethyl Phenyl Dimethyl SulphoniumNonaflate

[0059] 5.0 g (0.023 mole) of 4-Hydroxy-3,5-dimethyl phenyl dimethylsulphonium chloride was placed in a flask equipped with a condenser, athermometer, and a mechanical stirrer. 45 g of water and 0.92 g ofsodium hydroxide were added, and an intense color appeared. Dimethylsulphate (2.2 ml) was added at room temperature and the mixture washeated at 60° C. for 10 minutes. The solution changed to almostcolorless. The heating was stopped after 15 minutes and the solution wascooled to room temperature. 7.78 g of potassium perfluoro butanesulfonate in acetone(50 ml) was added drop wise and mixed for 2 hours.It was extracted with dichoromethane and the dicholoromethane layer waswashed with water, dried over sodium sulfate, and filtered. The solutionwas drowned into ether, and the-precipitate formed was filtered anddried in the vacuum dryer at less than 40° C. The solid product gave thefollowing analytical results: ¹H NMR(Acetone-d6), 2.32 (s, 6H, 2CH₃);3.4 (s, 6H, 2CH₃); 3.85 (s, 3H, OCH₃); 7.78 (s, 2H, aromatic). Theabsorptivity is 32.82 L/g.cm.

Synthetic Example 7 4-Methoxy Benzyl Dimethyl Sulphonium Triflate

[0060] 4-Methoxy benzyl mercaptan (25.0 g, 0.16 mole) was added to a 250ml round bottom flask with an overhead stirrer, a condenser, and athermometer. 50 g THF and 12.5 g of NaOH in water (50%) were added.Dimethyl sulphate (20.18 g, 0.16 mole, 15.2 ml) was added very slowlywith a syringe. The mixture was stirred at room temperature for 20minutes and then heated at 55° C. for 90 minutes. Silvertrifluoromethane sulfonate (41 g, 0.16 mole) was added and the silversalt was precipitated out. After filtering the salt, the solution wasdiluted with acetone and water, extracted with ether, and the aqueouslayer was extracted with dichloromethane. The dichloromethane layer waswashed with water, dried over sodium sulphate and drowned in ether. Aprecipitate was formed, which was filtered and washed with ether. It wasdried under vacuum. The solid product gave the following analyticalresults: 1H NMR(DMSO-d6), 2.75 (s, 6H, 2CH3);3.80 (s, 3H, OCH3); 4.61(s, 2H, CH2); 6.85-7.45 (m, 4H, aromatic).

Synthetic Example 8 Poly(t-butyl Norbornenecarboxylate-co-mevaloniclactone Methacrylate-co-2-methyladamantylMethacrylate-co-maleic Anhydride)

[0061] A hybrid copolymer was synthesized by reacting 126.45 g oft-butyl norbornene carboxylate (BNC), 129.2 g of mevaloniclactonemethacrylate (MLMA) and 152.73 g of 2-methyladamantyl methacrylate(MAdMA) and 191.78 g of maleic anhydride(MA) in presence of 5 weight% ofAIBN in tetrahydrofuran(THF) at 50% solid. The reaction was carried outfor 8 hours and the polymer was isolated from diethyl ether twice(1/10v/v ratio). The weight average molecular weight (Mw) as measured on aGel Permeation Chromatograph (GPC) using polystyrene standards and THFsolvent, was 5780.

Synthetic Example 9 Poly(2-methyladamantylMethacrylate-co-mevaloniclactone Methacrylate)

[0062] Polymerization was carried out using a feed of 1:1 molar ratio of

[0063] MAdMA and MLMA in tetrahydrofuran (THF) (25% solids) using AIBNinitiator (10 weight% with respect to monomers) at 70° C. under nitrogenatmosphere. The reaction mixture was stirred at 70° C. for 5 hours. Thepolymer solution was poured into methanol after the reaction wasfinished. The white powder was filtered, dissolved in THF (30% solids)again and re-precipitated, filtered and dried under vacuum untilconstant weight was obtained. The polymerization yield was about 65%.The Mw and number average molecular weight (Mn) as measured on a GPCusing polystyrene standards and THF solvent were 14000 and 8000,respectively.

Comparative Example 1

[0064] 1.5222 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate) of Synthetic Example 9, 0.0514 g (60 μmol/g) oftriphenylsulfonium nonafluorobutanesulfonate (absorptivity 117.74L/g.cm), 0.1444 g of 1 weight% ethyl lactate solution of diethanolamineand 0.018 g of 110 ppm ethyl lactate solution of a surfactant (FC-430,fluoroaliphatic polymeric ester, supplied by 3M Corporation, St. PaulMinn.) were dissolved in 13.26 g of ethyl lactate to give a photoresistsolution. The n & k values at 193 nm for this photoresist film were1.7287 and 0.02432, respectively. Separately, a silicon substrate coatedwith a bottom antireflective coating (B.A.R.C.) was prepared by spincoating the bottom anti-reflective coating solution (AZ® EXP ArF-1B.A.R.C. available from Clariant Corporation, Somerville, N.J.) onto thesilicon substrate and baking at 175° C. for 60 sec. The B.A.R.C filmthickness was 39 nm. The photoresist solution was then coated on theB.A.R.C coated silicon substrate. The spin speed was adjusted such thatthe photoresist film thickness was 330 nm. The photoresist film wasbaked at 115° C. for 60 sec. The substrate was then exposed in a 193 nmISI ministepper (numerical aperture of 0.6 and coherence of 0.7) using achrome on quartz binary mask. After exposure, the wafer waspost-exposure baked at 110° C. for 60 sec. The imaged photoresist wasthen developed using a 2.38 weight% aqueous solution of tetramethylammonium hydroxide for 60 sec. The line and space patterns were thenobserved on a scanning electron microscope. The photoresist had aphotosensitivity of 20 mJ/cm² and a linear resolution of 0.12 μm. Theline edge roughness (3σ) as measured on a KLA8100 CD SEM for 130 nm L/S(1: 1 pitch at best focus) was 12 nm.

Comparative Example 2

[0065] 26.05 g of polymer of Synthetic Example 8, 0.820 g (56 μmol/g) oftriphenylsulfonium nonafluorobutanesulfonate (absorptivity 117.74L/g.cm), 13.4g of 1 weight% propylene glycol monomethyl ether acetate(PGMEA) solution of 1,3,3-trimethyl-6-azabicyclo(3.2.1)octane and 0.24gof 10 weight% propyleneglycol monomethyether acetate (PGMEA) solution ofa surfactant (FC-430, fluoroaliphatic polymeric ester, supplied by 3Mcorporation, Minnesota) were dissolved in 159.5 g of PGMEA. The solutionwas filtered using 0.2 μm filter and processed in a similar manner tothat described in Comparative Example 1 except the photoresist film wasbaked at 110° C. for 90 sec, post-exposure baked at 130° C. for 90 secand development was carried out for 30 sec. The n & k values at 193 nmwere 1.7108 and 0.028, respectively. The photoresist had aphotosensitivity of 17 mJ/cm² and a linear resolution of 0.09 μm. Theline edge roughness (3σ) as measured on a KLA8100 CD SEM for 130 nm L/Swas 11 nm (130 nm, 1:2 pitch at best focus).

Comparative Example 3

[0066] 43.92 g of the polymer as in Synthetic Example 8, 0.11234 g ofdimethyl, p-methoxyphenyl sulfonium nonafluorobutanesulfonate (SynthesisExample 6), 1.622 g of 1% PGMEA solution of3-trimethyl-6-azabicyclo[3.2.1]octane, and 0.036 g of 10 weight%propyleneglycol monomethyether acetate (PGMEA) solution of a surfactant(fluoroaliphatic polymeric ester, supplied by 3M corporation, Minnesota)were dissolved in 24.30 g of PGMEA. The solution was filtered using 0.2μm filter and processed in a similar manner to that described inComparative Example 2. The n&k values at 193 nm were 1.7158 and 0.01670respectively. The photoresist had a sensitivity of 80 mJ/cm² and alinear resolution of 0.09 μm. The line edge roughness (3σ) as measuredon a KLA8100 CD SEM for 130 nm L/S was 5 nm (130 nm, 1:2 pitch at bestfocus).

Comparitive Example 4

[0067] 1.544 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate) as in Synthetic Example 9, 0.0295 g (60 μmol/g) ofdimethyl, p-methoxyphenyl sulfon iu m nonafluorobutanesulfonate(Synthesis Example 6), 0.1461 g of 1 weight% ethyl lactate solution ofdiethanolamine and 0.018 g of 120 ppm ethyl lactate solution of asurfactant (FC-430, fluoroaliphatic polymeric ester, supplied by 3MCorporation, St. Paul Minn.) were dissolved in 13.26 g of ethyl lactateto give a photoresist solution. The photoresist was processed in asimilar way to comparative example 1. The n& k values at 193 nm were1.7294 and 0.012716, respectively. The photoresist had aphotosensitivity of 63 mJ/cm² and a linear resolution of 0.12 μm. Theline edge roughness (3c) as measured on a KLA8100 CD SEM for 130 nm L/S(1:1 pitch, best focus) was 5 nm.

Example 1

[0068] 2.5527 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate) as in Synthetic Example 9, 0.0431 g (30 μmol/g) oftriphenylsulfonium nonafluorobutane sulfonate, 0.0244 g (30 μmol/g) ofdimethyl, p-methoxyphenyl sulfonium nonafluorobutanesulfonate, 0.4831 gof 1 weight% ethyl lactate solution of diethanolamine and 0.03 g of 10weight% ethyl lactate solution of a surfactant (fluoroaliphaticpolymeric ester, supplied by 3M Corporation, St. Paul Minn.) weredissolved in 21.887 g of ethyl lactate to give a photoresist solution.The photoresist was processed in a similar manner to comparativeexample 1. The photoresist had n and k values of 1.7120 and 0.017respectively. The photoresist had a photosensitivity of 34 mJ/cm² and alinear resolution of 0.12 μm. The line edge roughness (3σ) as measuredon a KLA8100 CD SEM for 130 nm L/S was 5.5 nm, which was a 54%improvement in line edge roughness over Comparative Example 1.

Example 2

[0069] 2.5506 g of the polymer as in Synthetic Example 8, 0.0430 g oftriphenylsulfonium nonafluorobutanesulfonate, 0.0244 g of dimethyl,p-methoxyphenyl sulfonium nonafluorobutanesulfonate, 0.7036 g of 1%PGMEA solution of 3-trimethyl-6-azabicyclo[3.2.1]octane, and 0.03 g of10 weight% propyleneglycol monomethyether acetate (PGMEA) solution of asurfactant (fluoroaliphatic polymeric ester, supplied by 3M corporation,Minnesota) were dissolved in 21.65 g of PGMEA. The solution was filteredusing 0.2 μm filter and processed in a similar manner to that describedin Comparative Example 2. The photoresist had n&k values of 1.7144 and0.023088 respectively. The photoresist had a sensitivity of 22 mJ/cm²and a linear resolution of 0.09 μm. The line edge roughness (3σ) asmeasured on a KLA8100 CD SEM for 130 nm L/S was 6.2 nm, which was a 44%improvement in line edge roughness over Comparative Example 2.

Example 3

[0070] 2.7401 g of the polymer as in Synthetic Example 8, 0.0694 g oftriphenylsulfonium nonafluorobutanesulfonate, 0.0523 g of dimethyl,p-methoxyphenyl sulfonium nonafluorobutanesulfonate, 1.3227 g of 1%PGMEA solution of 3-trimethyl-6-azabicyclo[3.2.1]octane, and 0.03 g of10 weight% propyleneglycol monomethyether acetate (PGMEA) solution of asurfactant (fluoroaliphatic polymeric ester, supplied by 3M corporation,Minnesota) were dissolved in 20.78 g of PGMEA. The solution was filteredusing 0.2 μm filter and processed in a similar manner to that describedin Comparative Example 2. The photoresist had a photosensitivity of 21mJ/cm² and a linear resolution of 0.09 μm. The line edge roughness (3σ)as measured on a KLA8100 CD SEM for 130 nm L/S was 6.2 nm, which was a46% improvement in line edge roughness over Comparative Example 2.

Example 4

[0071] 2.5507 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate) as in Synthesis Example 9, 0.0431 g oftriphenylsulfonium nonafluorobutane sulfonate, 0.0288 g of cyclohexyl,2-oxocyclohexyl, methyl sulfonium trifluoromethane sulfonate(absorptivity 3.32 L/g.cm), 0.2414 g of 1 weight% ethyl lactate solutionof diethanolamine and 0.03 g of 10 weight% ethyl lactate solution of asurfactant (fluoroaliphatic polymeric ester, supplied by 3M Corporation,St. Paul Minn.) were dissolved in 22.1 g of ethyl lactate to give aphotoresist solution. The photoresist was processed in a similar mannerto comparative example 1. The photoresist had a photosensitivity of 23mJ/cm² and a linear resolution of 0.12 μm. The line edge roughness (3σ)as measured on a KLA8100 CD SEM for 130 nm L/S was 5.5 nm, which was a54% improvement in line edge roughness over Comparative Example 1.

Example 5

[0072] 2.5548 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate), 0.0431 g of triphenylsulfonium nonafluorobutanesulfonate, 0.0288 g of bis(phenylsulfonyl)diazomethane (absorptivity169.49 L/g.cm) from Midori Kagaku Company, 0.2417 g of 1 weight% ethyllactate solution of diethanolamine and 0.03 g of 10 weight% ethyllactate solution of a surfactant (fluoroaliphatic polymeric ester,supplied by 3M Corporation, St. Paul Minn.) were dissolved in 22.1 g ofethyl lactate to give a photoresist solution. The photoresist wasprocessed in a similar manner to comparative example 1. The photoresisthad a photosensitivity of 24 mJ/cm² and a linear resolution of 0.13 μm.The line edge roughness (3σ) as measured on a KLA8100 CD SEM for 130 nmL/S was 7.0 nm, which was a 41% improvement in line edge roughness overComparative Example 1.

Example 6

[0073] 2.5496 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate), 0.0430 g of triphenylsulfonium nonafluorobutanesulfonate, 0.0288 g of [bis(p-chlorophenylsulfonyl)diazomethane](absorptivity 146.49 L/g.cm) from Midori Kagaku Company, 0.2413 g of 1weight% ethyl lactate solution of diethanolamine and 0.03 g of 10weight% ethyl lactate solution of a surfactant (fluoroaliphaticpolymeric ester, supplied by 3M Corporation, St. Paul Minn.) weredissolved in 22.1 g of ethyl lactate to give a photoresist solution. Thephotoresist was processed in a similar manner to comparative example 1.The formulation had a sensitivity of 23 mJ/cm² and a linear resolutionof 0.12 μm. The line edge roughness (3σ) as measured on a KLA8100 CD SEMfor 130 nm L/S was 7.5 nm, which was a 38% improvement in line edgeroughness over Comparative Example 1.

Example 7

[0074] 2.5556 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate), 0.0431 g of triphenylsulfonium nonafluorobutanesulfonate, 0.0239 g of [5-Norbornene-2,3-trifluoromethanesulfonimide](absorptivity 71.42 L/g.cm) from Midori Kagaku Company, 0.2418 g of 1weight% ethyl lactate solution of diethanolamine and 0.03 g of 10weight% ethyl lactate solution of a surfactant (fluoroaliphaticpolymeric ester, supplied by 3M Corporation, St. Paul Minn.) weredissolved in 22.1 g of ethyl lactate to give a photoresist solution. Theresist was processed similar to comparative example 1. The formulationhad a sensitivity of 21 mJ/cm² and a linear resolution of 0.13 μm. Theline edge roughness (3σ) as measured on a KLA8100 CD SEM for 130 nm L/Swas 7.8 nm, which was a 35% improvement in line edge roughness overComparative Example 1.

Example 8

[0075] 2.5512 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate), 0.0430 g of triphenylsulfonium nonafluorobutanesulfonate, 0.0283 g of [4,5-dihydroxy-1-napthalene dimethylsulfoniumtrifluoromethane sulfonate] (absorptivity 50.62 L/g.cm)from MidoriKagaku Company, 0.2414 g of 1 weight% ethyl lactate solution ofdiethanolamine and 0.03 g of 10 weight% ethyl lactate solution of asurfactant (fluoroaliphatic polymeric ester, supplied by 3M Corporation,St. Paul Minn.) were dissolved in 22.1 g of ethyl lactate to give aphotoresist solution. The photoresist was processed in a similar manneras comparative example 1. The photoresist had a photosensitivity of 21mJ/cm² and a linear resolution of 0.13 μm. The line edge roughness (3%)as measured on a KLA8100 CD SEM for 130 nm L/S was 8.0 nm, which was a33% improvement in line edge roughness over Comparative Example 1.

Example 9

[0076] 2.5512 g of poly(2-methyladamantyl methacrylate-co-2-mevaloniclactone methacrylate), 0.0430 g of triphenylsulfonium nonafluorobutanesulfonate, 0.0283 g of [4,6-dihydroxy-1-napthalene dimethylsulfoniumtrifluoromethane sulfonate] (absorptivity 60.34 L/g.cm) from MidoriKagaku Company, 0.2414 g of 1 weight% ethyl lactate solution ofdiethanolamine and 0.03 g of 10 weight% ethyl lactate solution of asurfactant (fluoroaliphatic polymeric ester, supplied by 3M Corporation,St. Paul Minn.) were dissolved in 22.1 g of ethyl lactate to give aphotoresist solution. The photoresist was processed in a similar mannerto comparative example 1. The photoresist had a photosensitivity of 0.22mJ/cm² and a linear resolution of 0.13. The line edge roughness (3σ) asmeasured on a KLA8100 CD SEM for 130 nm L/S was 7.5 nm, which was a 38%improvement in line edge roughness over Comparative Example 1.

1. A photoresist composition useful for imaging in deep uv comprising;a) a polymer containing an acid labile group; and, b) a mixture ofphotoactive compounds, where the mixture comprises a lower absorbingcompound selected from structure 1 and 2, and a higher absorbingcompound selected from structure 4 and 5,

where, R₁ and R₂ are independently (C₁-C₆)alkyl, cycloalkyl,cyclohexanone, R₅-R₉ are independently hydrogen, hydroxyl, (C₁-C₆)alkyl,C₁-C₆)aliphatic hydrocarbon containing one or more O atoms, m=1-5, X⁻ isan anion, and Ar is selected from naphthyl, anthracyl, and structure 3,

where, R₃ is hydrogen or (C₁-C₆)alkyl, R₄ is independently hydrogen,(C₁-C₆)alkyl, (C₁-C₆)aliphatic hydrocarbon containing one or more Oatoms, Y is a single bond or (C₁-C₆)alkyl, and n=1-4.
 2. The compositionaccording to claim 1, where the compound of structure 1 is selected froma 4-methoxyphenyl-dimethylsulfonium salt,3,5-dimethyl-4-methoxyphenyl-dimethyl sulfonium salt,4-hydroxyphenyl-dimethyl sulfonium salt, and3,5-dimethyl-4-hydroxyphenyl-dimethyl sulfonium salt.
 3. The compositionaccording to claim 1, where the compound of structure 2 is selected from4-methoxyphenyl-methyliodonium salt,3,5-dimethyl-4-hydroxyphenyl-methyliodonium salt, 4-hydroxyphenyl-methyliodonium salt and 3,5-dimethyl-4-methoxyphenyl-methyliodonium salt. 4.The composition according to claim 1, where the compound of structure 4is selected from a triphenyl sulfonium salt and its derivatives.
 5. Thecomposition according to claim 1, where the compound of structure 5 isselected from a diphenyl iodonium salt and its derivatives.
 6. Thecomposition according to claim 1, where the polymer is nonaromatic. 7.The composition according to claim 1, where the molar ratio of thehigher absorbing compound to the lower absorbing compound is 2:1.
 8. Thecomposition according to claim 1, where the molar ratio of higherabsorbing compound to the lower absorbing compound is 1:2.
 9. A processfor imaging a photoresist comprising the steps of: a) forming on asubstrate a photoresist coating from the photoresist composition ofclaim 1; b) image-wise exposing the photoresist coating; c) optionally,postexposure baking the photoresist coating; and d) developing thephotoresist coating with an aqueous alkaline solution.
 10. The processof claim 9, where the image-wise exposure wavelength is below 200 nm.11. The process according to claim 9, where the aqueous alkalinesolution comprises tetramethylammonium hydroxide.
 12. The processaccording to claim 9, where the aqueous alkaline solution furthercomprises a surfactant.
 13. The process according to claim 9, where thesubstrate is selected from a microelectronic device and a liquid crystaldisplay substrate.